#include<iostream>
#include<vector>
#include<queue>
#include<cstring>
#include<cmath>
#include<map>
#include<set>
#include<cstdio>
#include<algorithm>
#define debug(a) cout<<#a<<"="<<a<<endl;
using namespace std;
const int maxn=3e3+1000;
typedef long long LL;
inline LL read(){LL x=0,f=1;char ch=getchar();	while (!isdigit(ch)){if (ch=='-') f=-1;ch=getchar();}while (isdigit(ch)){x=x*10+ch-48;ch=getchar();}
return x*f;}
LL a[maxn];
char s[maxn];
int main(void){
   cin.tie(0);std::ios::sync_with_stdio(false);
   LL t;cin>>t;
   while(t--){
        LL n;cin>>n;

        for(LL i=0;i<=n+10;i++) a[i]=0;
        for(LL i=1;i<=n;i++) cin>>s[i];
        for(LL i=1;i<=n;i++) a[i]=(s[i]-'0');
        vector<LL>ans;
        LL flag=1;
        for(LL i=n;i>=1;i--){
            if(flag==1&&(a[i]&1) ) { ans.push_back(a[i]);flag++;}
            else if(flag==2&&(a[i]&1)){
                 ans.push_back(a[i]);
                 flag++;
            }
        }
        reverse(ans.begin(),ans.end());
        if(ans.size()<2){
          cout<<"-1"<<"\n";
        }
        else{
          for(auto i:ans){
            cout<<i;
          }
          cout<<"\n";
        }
   }
   return 0;
}
